You might have seen International Women's Day mentioned in the media or heard friends talking about it. But what is it for? When is it? Is it a celebration or a protest? And is there an equivalent International Men's Day?

For more than a century people around the world have been marking this day. Read on to find out why.

1. When did it all start?

International Women's Day grew out of the labour movement to become a UN-recognised annual event.

The seeds of it were planted in 1908, when 15,000 women marched through New York City demanding shorter working hours, better pay and the right to vote. It was the Socialist Party of America who declared the first National Woman's Day, a year later.The idea to then make the day international came from a woman called Clara Zetkin. She suggested the idea in 1910 at an International Conference of Working Women in Copenhagen. There were 100 women there, from 17 countries, and they agreed unanimously.

It was first celebrated in 1911, in Austria, Denmark, Germany and Switzerland. The centenary was celebrated in 2011, so this year we're technically celebrating the 107th International Women's Day.

Things were made official in 1975 when the United Nations (UN) started celebrating the day and later set an annual theme. The first one (in 1996) was "Celebrating the past, Planning for the Future".

International Women's Day has become a date to celebrate how far women have come in society, in politics and in economics, while the political roots of the day mean strikes and protests are often organised to raise awareness of continued inequality.

2. When is it?

8 March. Clara Zetkin's initial idea for an International Women's Day had no fixed date and it wasn't formalised until a war-time strike in 1917 when Russian women demanded "bread and peace". Four days into the women's strike the Tsar was forced to abdicate and the provisional government granted women the right to vote. The date when the women's strike commenced on the Julian calendar, which was then in use in Russia, was Sunday 23 February. This day in the Gregorian calendar was 8 March - and that's when it's celebrated today.

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